1. Field of the Invention
The invention describes methods of making cross-linked total joint implants by controlling the spatial control of anti-cross-linking agents. The invention uses methods of extracting anti-cross-linking agents and controlling antioxidant concentrations in polymeric materials for joint implants.
2. Background of the Invention
Radiation cross-linking of polymers enhances many of their mechanical properties. For ultrahigh molecular weight polyethylene (UHMWPE), radiation cross-linking can also enhance its wear resistance under bi-directional motion similar to that experienced in human joints. However, radiation cross-linking can also decrease the toughness of UHMWPE with increasing radiation dose. Thus, controlling cross-linking spatially such that only portions of the polymer are cross-linked may be desirable to maintain the toughness of the material while improving its wear resistance.
Spatially controlling cross-linking in polymers can be performed in several ways; one approach is to use a spatial distribution of an additive in the polymer which can decrease cross-linking. This invention describes methods of extracting and/or incorporating additives in a polymeric material, for example, to spatially control the concentration profile of the additive in the polymeric material.